First official hydro release going in

* Using a local ros maven repo in the workspace/share/maven directories
* Pulls in external maven dependencies from https://github.com/rosjava/rosjava_maven_repo
* Installs - so is now rolling debs as soon as I finish this.
* Uses gradle plugins to avoid repetition of gradle build logic.
* Moves test_ros messages to rosjava_test_msgs.
* Gets package version information from package.xml
* Message generation and message generation code has been moved out (and under).

This is going into hydro - the old hydro branch has been tagged at 0.0.0.